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Examples:

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Wikipedia:

Flightless bird | Flightless birds

birds that lack the ability to fly. These species rely on running and/or swimming instead of flying, but evolved from flying ancestors. There are about forty species in existence today, the best known being the ostrich, emu, cassowary, rhea, kiwi, and ... (41 of 927 words, 7 images)

ratite

Wiktionary:

ratite | ratites [plural]

A bird of the order of Struthioniformes, a diverse group of large running, flightless birds, mostly extinct, but including the cassowary, elephant bird, emu, kiwi, moa, ostrich, rhea and tinamou (30 of 31 words)

Random House Dictionary:

ratite

Macmillan British Dictionary:

bird[countable] | birds [plural] | be strictly for the birds | a bird in the hand is worth two in the bush | the birds and the bees | birds of a feather flock together | do bird | give someone the bird

an animal covered in feathers, with two wings for flying and a hard pointed ... | [British, informal] a young woman. Some people find this word ... (25 of 195 words, 9 definitions, 2 usage examples, pronunciation)